All I know is, I have seen in the catalog, Brownells' makes a PRODUCT called "Additive S" for hot bluing tanks that supposedly prevents this. ADDENDUM: I found this on the Ruger Website "Ruger firearms is not the only one noted for turning purple. Winchester 94s after a certain serial number had a change in the metal alloy used in the receivers and would turn purple. When I was bluing guns years ago, I used Brownell's Oxnate #7 bluing salts and the "S" additive to get around that problem."
From the BROWNELL CATALOG
Special Additive For Bluing Heat-Treated Steels & Cast Irons
Something we all have been looking for - for a long time. Prevents red colors from forming on heat-treated steels; makes possible the bluing of 95% of all cast irons. Prevents bath breakdown when a little copper is present, or a little brazing has been done. Produces deeper color. Shortens in-tank time, increases production. Maintains corrosion resistance of the bluing. Altho' it appears a little expensive in the undiluted state, 1 pint will treat up to 8 gallons (at 2 oz. per gallon), or 2 operating bluing tanks of Oxynate No. 7™. So - in the long haul - Oxynate "S" is one of the cheapest additions you can make to your bluing setup. Full, detailed instructions. Must be added when no guns in tank; wait 30 minutes before bluing.
Big Book Catalog, Issue:67, Page:416
GOOD LUCK
Jerry
